9 Feb
2006
9 Feb
'06
2:59 a.m.
"Julian Wolfe (FireflyST)" <fireflyst at earthlink.net> wrote:
Okay, what I immediately noticed is that these
machines say "MP" and Don's panel doesn't.
More differences: Don's panel have the location for the key moved to the
other side of the parity lamps. Which is rather weird.
Also, the screenprint of 11/74 looks shadowed, which is weird. And the
right hand side have a different color than the left hand side.
And of course, the 11/74s from Tim don't have any CIS stuff on the front
panel.
(I'm still thinking that Don's panel have never had a matching piece of
real hardware, since I don't think that CPU was ever built.)
Tim's picture however are of a real machine. Don't know which one,
though. If it's just a two CPU machine, it might have been POLLUX::,
since CASTOR:: was four CPUs. However, other machine have existed in the
past.
Were there non-multiprocessor 11/74s? If so, what
would have been the benefits over 11/70s?
Yes there were. And the benifits were none. Actually, they were slightly
worse than normal 11/70s, but the difference were minimal.
After DEC decided to not make the 11/74 into a commercial product, they
used 11/74 parts for 11/70 machines. Atleast inhouse. Not sure if any of
those parts found their way into customers machines.
Used as such, the differences were basically related to cache: The MMU
have the cache bypass bit. The ASRB instruction always bypass the cache,
and you can also order the machine to explicitly bypass the cache
(unless my memory fails me).
But nothing of this was used by any OS normally, so the only thing
noticeable would be the slower ASRB instruction.
Johnny
-----Original Message-----
>From: Tim Shoppa <tshoppa at wmata.com>
>Sent: Feb 8, 2006 12:24 PM
>To: cctalk at classiccmp.org
>Subject: Re: Original 11/74 front panel
>
>Don North wrote
>
>>So how many of these panels exist is hard to say. I know only of one.
>
>Two more can be seen at
>
> http://www.trailing-edge.com/~shoppa/1174Xopen.jpg
>
>So that makes three :-).
>
>Tim.
--
Johnny Billquist || "I'm on a bus
|| on a psychedelic trip
email: bqt at update.uu.se || Reading murder books
pdp is alive! || tryin' to stay hip" - B. Idol
9 Feb
9 Feb
3:07 a.m.
"Julian Wolfe (FireflyST)" <fireflyst at
earthlink.net> wrote:
I think that was an artifact of scanning it.
Gordon.
Okay, what I immediately noticed is that these
machines say "MP" and
Don's panel doesn't.
More differences: Don's panel have the location for the key moved to the
other side of the parity lamps. Which is rather weird.
Also, the screenprint of 11/74 looks shadowed, which is weird. And the
right hand side have a different color than the left hand side. 
11:37 a.m.
gordonjcp at gjcp.net wrote:
Completely true. This is not a digital photograph, but I put the panel
on a flatbed scanner with a 14" max capability. Since the panel is over
14" wide I had to scan it in two pieces and merge them; that accounts
for the vertical line artifact between the main lights and the switches
on the righthand side. One of these days I'll take a better single view
digital picture.
Don
"Julian
Wolfe (FireflyST)" <fireflyst at earthlink.net> wrote:
I think that was an artifact of scanning it.
Gordon.
Okay, what I immediately noticed is that these
machines say "MP" and
Don's panel doesn't.
More differences: Don's panel have the location for the key moved to
the
other side of the parity lamps. Which is rather weird.
Also, the screenprint of 11/74 looks shadowed, which is weird. And the
right hand side have a different color than the left hand side.
12:01 p.m.
Johnny Billquist wrote:
"Julian Wolfe (FireflyST)" <fireflyst at
earthlink.net> wrote:
Besides moving the keyswitch, the dial selector knobs on the righthand
side were moved around as well to make space to label all the extra
switch positions.
As I mentioned in another reply, the artifacts are due to scanning the
panel on a 14" flatbed scanner in two pieces, and merging the scans.
When I get around to it I'll take a high quality single-view photograph.
Okay, what I immediately noticed is that these
machines say "MP" and
Don's panel doesn't.
More differences: Don's panel have the location for the key moved to
the other side of the parity lamps. Which is rather weird.
Also, the screenprint of 11/74 looks shadowed, which is weird. And the
right hand side have a different color than the left hand side.
And of course, the 11/74s from Tim don't have any CIS stuff on the
front panel. (I'm still thinking that Don's panel have
never had a matching piece
of real hardware, since I don't think that CPU was ever built.)
I can only say
that I worked on real 11/74 hardware in 1978-9 writing
microcode for the 11/74 CIS (commercial instruction set) accelerator
(packed decimal, string instructions, etc). See
http://www.bitsavers.org/pdf/dec/pdp11/1174/Prelim_KB11-E_Diffs_Aug78.pdf
for a memo written by Ray Boucher, one of the hardware designers (Al,
how did you ever come across a memo such as this???). The other hardware
designed was Mike Brown. The other microcoders were Dave Sager and Lewis
Costas. The project manager was Dave Barry. How much more do you need to
know?
Not a lot of 11/74 CIS systems were built, probably no more than a dozen
or so maximum. The 11/74 folded in the 11/70MP changes which had been
done about a year earlier, so an 11/74 was really an 11/70MP base plus
the CIS option. Later when the 11/74 CIS was killed as a product, the
11/74 name lived on, but it was strictly a renamed version of the 11/70MP.
Tim's picture however are of a real machine. Don't know which one,
though. If it's just a two CPU machine, it might have been POLLUX::,
since CASTOR:: was four CPUs. However, other machine have existed in
the past.
All true statements. ASRB to memory was modified to act as the semaphore
instruction and thus always bypassed the cache AND did an atomic
read/modify/write cycle to the memory. The valid semaphore memory values
were 0 and 1; ASRB would then always set the memory value to 0 and
return the old value in the C-bit from the right shift carry out.
Were there non-multiprocessor 11/74s? If so,
what would have been
the benefits over 11/70s?
Yes there were. And the benifits were none. Actually, they were
slightly worse than normal 11/70s, but the difference were minimal.
After DEC decided to not make the 11/74 into a commercial product,
they used 11/74 parts for 11/70 machines. Atleast inhouse. Not sure if
any of those parts found their way into customers machines.
Used as such, the differences were basically related to cache: The MMU
have the cache bypass bit. The ASRB instruction always bypass the
cache, and you can also order the machine to explicitly bypass the
cache (unless my memory fails me).
But nothing of this was used by any OS normally, so the only thing
noticeable would be the slower ASRB instruction.
Johnny
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days inactive
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3 comments
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